Description: (Taken directly from the application) The formation of epithelial cell polarity is a fundamental process in embryonic development and organogenesis. Polarized epithelia form a physical barrier between the host and external environment essential for homeostasis. Cells of this type maintain distinct apical and basolateral membrane domains by actively regulating the membrane distribution of lipids and proteins as well as the submembraneous cytoskeleton unique to each surface. The apical plasma membrane usually contains proteins required for organ-specific functions. In epithelial cells, which line the lumen of kidney tubule segments, for example, many apical membrane proteins mediate absorption. The basolateral plasma membrane contains most of the "house-keeping" proteins necessary for executing basic cellular mechanisms, including growth regulatory molecules like the EGF receptor. A long-term goal of this project is to understand how different genes which cause polycystic kidney disease allow the EGF receptor to mislocalize to the apical plasma membrane in renal cysts originating in collecting tubules. We also wish to learn how apical EGF receptor mislocalization contributes to pathophysiology in this genetically diverse set of diseases, with an emphasis on autosomal recessive disease. This application has two broad Specific Aims. The first Specific Aim seeks to determine whether there is functional connection between ligand-induced trafficking of EGF receptors located at the apical plasma membrane and signaling output, using newly-developed conditionally immortalized collecting tubule cell lines. A long-term goal of this aim is to identify EGF receptor signaling pathways initiated from the apical surface which may be involved in polycystic kidney disease pathophysiology. The second Specific Aim seeks to define and understand protein interactions mediated by intrinsic motifs in the EGF receptor juxtamembrane domain important for regulating endocytic transport and/or signal transduction. This aim will be achieved with three complementary experimental approaches, using information gained from structural studies and in vitro binding studies to manipulate and analyze protein-protein interactions in vivo. A long-term goal of these studies is to identify novel therapeutic targets to control abnormal trafficking and signaling by EGF receptors mislocalized to the apical plasma membrane in cystic lesions. This project is a collaboration between a cell biologist with broad experience in EGF receptor trafficking and signaling, and a structural biologist experienced in structure-function studies.